Belt sanders are generally of two types. A portable tool is designed to be manipulated by the operator over the surface to be sanded. A stationary sander is designed to have the work manipulated relative the sanding machine.
Portable belt sanders are generally utilized to sand flat or slightly convex surfaces and generally have a flat platen fixed between a pair of rollers or pulleys, one at either end of the flat platen. A drive roll or pulley is provided which may comprise one of the two rolls adjacent the end of the platen or may be a yet third roll or pulley spaced apart therefrom. In portable sanders, a housing, drive motor and handle means are provided for grasping and manipulation by the operator. Usually a generally D shaped handle is provided at one end of the tool and the roller at the opposite end is freely rotatable, that is, comprises an idler roll or pulley that is movably supported relative the platen and spring biased outwardly thereof to provide tensioning of the belt. This idler pulley is generally retractable against the spring biasing to release tension and enable belt replacement. Also, one end of the idler pulley support shaft is generally pivoted to the spring biased support structure and separate means are provided for adjusting the angular orientation thereof to provide a tracking adjustment so that the belt runs true.
In stationary belt sanders, on the other hand, a spring biased tensioning mechanism for the idler roll is generally undesirable because sanding is often done on concave surfaces pressed against the moving belt as it traverses around the idler roll. In these machines, a positive adjustment is generally provided for both ends of the idler roll support shaft with both ends being positively adjustable to provide both tensioning of the belt and tracking adjustment therefore.
One form of support mechanism for such an idler roll or pulley of a stationary belt sander providing the track tension and tracking adjustments has employed the use of two parallel slidable pins attached in some manner pivotally at approximate right angles one each to the respective ends of the shaft carrying the idler roll or pulley. Substantial machining is necessary to provide both the pins and the track tension and tracking adjusting mechanisms. In U.S. Pat. No. 3,406,487, on the other hand, there is disclosed a substantially less expensive tensioning and tracking mechanism utilizing eye-bolts as the idler roll shaft supports. While this system offers certain advantages, such as relatively low cost, rapid and accurate adjustment thereof is difficult to achieve.